Switch proc_getlwpstatus from PT_LWPINFO to PT_GET_SIGINFO for NetBSD

PT_LWPINFO from FreeBSD is almost never intended to be expressed with
PT_LWPINFO in NetBSD. PT_GET_SIGINFO reads siginfo_t with

Switch proc_getlwpstatus from PT_LWPINFO to PT_GET_SIGINFO for NetBSD

PT_LWPINFO from FreeBSD is almost never intended to be expressed with
PT_LWPINFO in NetBSD. PT_GET_SIGINFO reads siginfo_t with the signal
information about the event, on FreeBSD siginfo_t is merged into
ptrace_lwpinfo and returns the thread that received the event (not the
first one in a list like on NetBSD).

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add a proc_getmodel() interface to return whether a process
is a 32-bit or 64-bit process. the interface is from freebsd
but the implementation is different.
needed by dtrace.

implement proc_getlwpstatus() for netbsd using PT_GET_SIGINFO.

the netbsd version of PT_LWPINFO is different from the freebsd version
in that we use lp_lwpid as an input to say which lwp to operate on.
freebsd passes the lwpid as the pid, which works fine there

the netbsd version of PT_LWPINFO is different from the freebsd version
in that we use lp_lwpid as an input to say which lwp to operate on.
freebsd passes the lwpid as the pid, which works fine there
since freebsd has globally unique LWP IDs which are also distinct
from process IDs. the libproc interface that uses this ptrace() call
is only supposed to return info for the process's representative LWP,
so just initialize pl_lwpid to 1 before using it.

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Fix the broken detach code and make the proc tests detach instead
of continue, so that we don't get kernel diagnostic messages about
detaching traced processes.

Add glue, adjust for NetBSD.

Import libproc from FreeBSD